Bug 1131557 - Serve multiple xpcom events in one poll iteration. r=mcmanus

modules/libpref/init/all.js

@@ -1359,6 +1359,12 @@ pref("network.http.enforce-framing.http1", false);
 pref("network.ftp.data.qos", 0);
 pref("network.ftp.control.qos", 0);
 
+// If this pref is false only one xpcom event will be served per poll
+// iteration. This is the original behavior.
+// If it is true multiple events will be served.
+pref("network.sts.serve_multiple_events_per_poll_iteration", true);
+// The max time to spend on xpcom events between two polls in ms.
+pref("network.sts.max_time_for_events_between_two_polls", 100);
 // </http>
 
 // 2147483647 == PR_INT32_MAX == ~2 GB

netwerk/base/nsSocketTransportService2.cpp

@@ -40,6 +40,8 @@ PRThread                 *gSocketThread           = nullptr;
 #define SOCKET_LIMIT_TARGET 550U
 #define SOCKET_LIMIT_MIN     50U
 #define BLIP_INTERVAL_PREF "network.activity.blipIntervalMilliseconds"
+#define SERVE_MULTIPLE_EVENTS_PREF "network.sts.serve_multiple_events_per_poll_iteration"
+#define MAX_TIME_BETWEEN_TWO_POLLS "network.sts.max_time_for_events_between_two_polls"
 
 uint32_t nsSocketTransportService::gMaxCount;
 PRCallOnceType nsSocketTransportService::gMaxCountInitOnce;
@@ -67,6 +69,9 @@ nsSocketTransportService::nsSocketTransportService()
     , mKeepaliveRetryIntervalS(1)
     , mKeepaliveProbeCount(kDefaultTCPKeepCount)
     , mKeepaliveEnabledPref(false)
+    , mServeMultipleEventsPerPollIter(true)
+    , mServingPendingQueue(false)
+    , mMaxTimePerPollIter(100)
     , mProbedMaxCount(false)
 {
 #if defined(PR_LOGGING)
@@ -481,6 +486,8 @@ nsSocketTransportService::Init()
         tmpPrefService->AddObserver(KEEPALIVE_IDLE_TIME_PREF, this, false);
         tmpPrefService->AddObserver(KEEPALIVE_RETRY_INTERVAL_PREF, this, false);
         tmpPrefService->AddObserver(KEEPALIVE_PROBE_COUNT_PREF, this, false);
+        tmpPrefService->AddObserver(SERVE_MULTIPLE_EVENTS_PREF, this, false);
+        tmpPrefService->AddObserver(MAX_TIME_BETWEEN_TWO_POLLS, this, false);
     }
     UpdatePrefs();
 
@@ -686,6 +693,12 @@ nsSocketTransportService::AfterProcessNextEvent(nsIThreadInternal* thread,
     return NS_OK;
 }
 
+void
+nsSocketTransportService::MarkTheLastElementOfPendingQueue()
+{
+    mServingPendingQueue = false;
+}
+
 #ifdef MOZ_NUWA_PROCESS
 #include "ipc/Nuwa.h"
 #endif
@@ -730,15 +743,39 @@ nsSocketTransportService::Run()
             // If there are pending events for this thread then
             // DoPollIteration() should service the network without blocking.
             DoPollIteration(!pendingEvents);
-            
+
             // If nothing was pending before the poll, it might be now
-            if (!pendingEvents)
+            if (!pendingEvents) {
                 thread->HasPendingEvents(&pendingEvents);
+            }
 
             if (pendingEvents) {
-                NS_ProcessNextEvent(thread);
-                pendingEvents = false;
-                thread->HasPendingEvents(&pendingEvents);
+                if (mServeMultipleEventsPerPollIter) {
+                    if (!mServingPendingQueue) {
+                        nsresult rv = Dispatch(NS_NewRunnableMethod(this,
+                            &nsSocketTransportService::MarkTheLastElementOfPendingQueue),
+                            nsIEventTarget::DISPATCH_NORMAL);
+                        if (NS_FAILED(rv)) {
+                            NS_WARNING("Could not dispatch a new event on the "
+                                       "socket thread.");
+                        } else {
+                            mServingPendingQueue = true;
+                        }
+                    }
+                    TimeStamp eventQueueStart = TimeStamp::NowLoRes();
+                    do {
+                        NS_ProcessNextEvent(thread);
+                        pendingEvents = false;
+                        thread->HasPendingEvents(&pendingEvents);
+                    } while (pendingEvents && mServingPendingQueue &&
+                             ((TimeStamp::NowLoRes() -
+                               eventQueueStart).ToMilliseconds() <
+                              mMaxTimePerPollIter));
+                } else {
+                    NS_ProcessNextEvent(thread);
+                    pendingEvents = false;
+                    thread->HasPendingEvents(&pendingEvents);
+                }
             }
         } while (pendingEvents);
 
@@ -982,6 +1019,20 @@ nsSocketTransportService::UpdatePrefs()
             mKeepaliveEnabledPref = keepaliveEnabled;
             OnKeepaliveEnabledPrefChange();
         }
+
+        bool serveMultiplePref = false;
+        rv = tmpPrefService->GetBoolPref(SERVE_MULTIPLE_EVENTS_PREF,
+                                         &serveMultiplePref);
+        if (NS_SUCCEEDED(rv)) {
+            mServeMultipleEventsPerPollIter = serveMultiplePref;
+        }
+
+        int32_t maxTimePref;
+        rv = tmpPrefService->GetIntPref(MAX_TIME_BETWEEN_TWO_POLLS,
+                                        &maxTimePref);
+        if (NS_SUCCEEDED(rv) && maxTimePref >= 0) {
+            mMaxTimePerPollIter = maxTimePref;
+        }
     }
     
     return NS_OK;

netwerk/base/nsSocketTransportService2.h

@@ -17,6 +17,7 @@
 #include "nsIObserver.h"
 #include "mozilla/Mutex.h"
 #include "mozilla/net/DashboardTypes.h"
+#include "mozilla/Atomics.h"
 
 class nsASocketHandler;
 struct PRPollDesc;
@@ -217,6 +218,10 @@ private:
     // True if TCP keepalive is enabled globally.
     bool        mKeepaliveEnabledPref;
 
+    bool                   mServeMultipleEventsPerPollIter;
+    mozilla::Atomic<bool>  mServingPendingQueue;
+    int32_t                mMaxTimePerPollIter;
+
     void OnKeepaliveEnabledPrefChange();
     void NotifyKeepaliveEnabledPrefChange(SocketContext *sock);
 
@@ -233,6 +238,8 @@ private:
     void DetachSocketWithGuard(bool aGuardLocals,
                                SocketContext *socketList,
                                int32_t index);
+
+    void MarkTheLastElementOfPendingQueue();
 };
 
 extern nsSocketTransportService *gSocketTransportService;